Hydraulic motor port design



Jan. 15, 1963 G. 1.. BROWN 3,073,659

I HYDRAULIC MOTOR PORT DESIGN Filed Sept. 21,- 1961 2 sheets-sheet 1 INVENTOR. GRAYDON L. BROWN ATTORNEY Jan. 15, 1963 G. L. BROWN 3,073,659

0 MOTOR PORT DESIG INVENTOR. 6R4 YOU/V L. BROWN A TTORNE Y United rates atent lice 3,073,659 HYDRAULIC MOTOR P031 DESTGN Graydon L. Brown, Ponca City, Okla, assignor to floutineutal Oil Company, Ponca City, Gkla, a corporation of Delaware Filed Sept. 21, 1961, Ser. No. 139,754 3 Claims. (til. 399-2) The present invention relates. to hydraulic motors, and more particularly, but not by way of limitation, relates to an improved port for a linear actuator designed to utilize high fluid pressures to reciprocate a massive load at high frequencies.

Considerable effort has been made in the oil industry to improve systems for seismographic surveying of subsurface geological strata. One system which has been used with marked success utilizes a device which imparts high energy vibration signals into the ground by means of a high energy transducer instead of by means of the more conventional explosive charge. This vibration signal is usually of a controlled frequency content for positive identification and usually is uniformly varied from approximately twenty cycles per second to one hundred cycles per second over a period of only a few seconds. One transducer device for imparting the vibratory energy to the earth is comprised of a large mass which is reciprocated at the desired frequency by a linearly reciprocating hydraulic motor. In this type transducer, either the piston or the cylinder of the motor is connected to the mass and the other of the two members of the hydraulic motor is connected to a platform which is pressed against the ground. When the mass is reciprocated relative to the platform at a high rate by the introduction of hydraulic fluid to the motor, the mass is reciprocated along a vertical axis. The force required to decelerate the mass at the bottom of the downstroke and then to accelerate the mass at the start of the upstroke is transmitted through the hydraulic fluid to the element of the motor which is connected to the platform resting on the earth so that the force is transmitted into the earth. The frequency of reciprocation of the motor is controlled by an electrically actuated four-way hydraulic valve and by suitable electrical circuit means for shifting the valve.

The hydraulic linear actuator heretofore used for reciprocating the mass in this type of transducer showed a marked reduction in the energy imparted to the earth at frequencies above eighty cycles per second. A graphical plot of the energy imparted to the ground as a function of frequency would show a sharp rise to a maximum at approximately twenty cycles per second and remain substantially constant until approximately eighty cycles per second, at which point the energy transmitted to the ground would sharply decline. This poor frequency response of the transducer device was attributable to the compressibility of the hydraulic fluid used to drive the linear actuator or hydraulic motor. By Way of example,

the weight of the mass in this transducer may be on the order of two tons and the fluid pressure utilized within the hydraulic motor on the order of 3,000 p.s.i. At these high pressures and high frequencies, the hydraulic fluid, which is normally considered incompressible, is compressible to such an extent that the fluid acts as a spring when applied to decelerate and accelerate the mass. The hydraulic fluid is compressed to such an extent that, at higher reciprocation frequencies, the acceleration or deceleration of the mass, as the case may be, is retarded. In other words, on the downstroke of the mass, the mass continues downward and compresses the fluid for a short period after the high pressure has been applied to oppose the inertial force of the mass and to start the mass moving upwardly again. The same compression of the hydraulic fluid occurs at the top of the stroke. At the higher frequencies, the control valve must switch before the mass can be accelerated to the maximum desired velocity necessary to produce the desired energy transmission to the ground. The net result is that the length of the stroke, and therefore the maximum velocity to which the piston is accelerated relative to the cylinder, is reduced with a corresponding reduction in the amount of energy imparted to the ground. The extent to which the hydraulic fluid is compressed, and, consequently the frequency response of the transducer reduced, is directly related to the volume of hydraulic fluid subjected to the maximum pressure.

In accordance with the present invention, the spring effect which the compressibility. of the hydraulic fluid creates is materially reduced by reducing the volume of hydraulic fluid within the porting system at each end of the cylinder between the piston and the four-way control valve, and yet maintaining the cross-sectional area of the flow path of the hydraulic fluid through the port system substantially constant so as not to interfere with the flow of hydraulic fluid to and from the interior of the motor. More specifically, the present invention contemplates the use of an annular groove machined in the cylinder means in such a manner as to be eccentric with respect to the piston rod. The eccentric groove is in fluid communication with the port through the cylinder wall and also is in circumferential communication with an annular passage leading to the face of the piston of the hydraulic motor.

Therefore, it is an important object of the present invention to increase the energy which can be imparted to the ground by a hydraulically actuated transducer of the type described at higher reciprocation frequencies.

Another object of the present invention is to provide an inexpensive porting system requiring no close tolerance machining which will materially reduce the volume of fluid in the porting system While maintaining substantially a constant cross-sectional area for nonrestricted flow of the hydraulic fluid into the interior of the cylinder.

Additional objects and advantages will be evident from the following detailed description and drawings wherein:

FIGURE 1 is a longitudinal cross section of a hydraulic linear actuator with the piston rod in full View illustrating an improved porting means in accordance with the present invention.

FIGURE 2 is a transverse cross section of the hydraulic linear actuator of FIG. 1 taken through the cylinder head along reference line 22.

FIGURE 3 is a partial cross-sectional view of a hydraulic linear actuator in which the cylinder is connected to the reciprocated mass and in which improved hydraulic fluid porting in accordance with the present invention is employed.

FIGURE 4 is a partial cross-sectional view of the hydraulic linear actuator of FIG. 3 taken along the reference line '4-4.

Referring now to FIGS. 1 and 2, a hydraulic linear actuator or hydraulic motor indicated generally by the reference numeral it) is comprised of a double-rod-end piston 12 reciprocally disposed within a cylinder indicated generally by the reference numeral 14. The piston has piston rods 12a and 12b extending in opposite directions through the ends of the cylinder 14. The rod 12a may be connected in a suitable manner to an electronic feedback control means (not shown) which acts in concert with any well-known four-way valve switching means (not shown) for maintaining the piston 12 within certain travel limits in the cylinder 14. The end of the rod 12b may be connected to the mass referred to in the introductory material above which is to be reciprocated. The piston 12 is provided with suitable conventional pis- 3 ton rings and has two faces 16 of equal areas which are exposed to hydraulic fluid.

The cylinder 14 is comprised of a tubular sleeve 18 having an upper cylinder head 20 and a lower cylinder head 22 threaded into the opposite ends thereof. Lock nuts 24 and 26 may be used to securely lock the cylinder heads 28 and 22, respectively, against rotation and loosening. The lock nuts 24 and 26 may be provided with set screws 28 and 36), respectively, to hold the lock nuts in place. The threaded couplings between the cylinder heads 28 and 22 and the sleeve 13 may be sealed by suitable O-rings 32 and 34. Identical packing assemblies are provided in each of the cylinder heads 20 and 22 and each comprises a spacer ring 36, a packing ring 38, and a threaded insert 49 for compressing the packing ring 38. The cylinder head 22 may be provided with a flange 42 for coupling the cylinder to the platform which engages the ground as described in the introductory material above.

The porting system in accordance with the present invention is provided in both of the cylinder heads 20 and 22. A cross section of the porting is shown in FIG. 2 and is equally accurate for a view considered as taken through either of the cylinder heads 20 or 22, but for convenience of discussion, FIG. 2 will be considered as taken on the reference line 22 through the head 20. The cylinder head 20 has a cylindrical bore 43 which extends radially through the cylinder head wall with respect to the axis of the piston rod 12a and also with respect to the axis of the cylinder 14. The internal diameter of the cylinder head 20 is greater than the external diameter of the piston rod 12a through the distance 44 so that an annular passageway 46 is defined between the cylinder head 20 and the rod 12a which communicates with one face 16 of the piston 12. A groove 48 is machined or otherwise formed around the internal circumference of the cylinder head 20 and is eccentric to the axis of both the piston rod 12a and the cylinder head 20, substantially as shown in FIG. 2. The eccentric groove 48 intersects the innermost end of the radial bore 43 and is also in circumferential communication with the annular passageway 46, as best seen in FIG. 2. The outermost end of the bore 43 is connected by suitable conduit means to the four-way control valve and then to a source of hydraulic fluid under pressure. The crosssectional area of the bore 43, which is circular in shape, is preferably substantially equal to the cross-sectional area of the annular passageway 46, which is in communication with the piston face 16. It will be noted that the width of the eccentric groove 48 is substantially equal to the diameter of the bore 43. The depth or the eccentricity of the groove 48 with respect to the axis of the rod 12a and the diameter of the groove 48 are selected so that the total cross-sectional area generally through the lines 12-17 and cc (FIG. 2) is substantially equal to the cross-sectional area of the bore 43 taken on line a-a which, in turn, as previously mentioned, is equal to the cross-sectional area of the annular passageway 46.

Referring now to FIGS. 3 and 4, which show another type of hydraulic linear actuator utilizing the porting concepts of the present invention, the hydraulic linear actuator is indicated generally by the reference numeral 50. A cylinder sleeve 52 is contained within a cylindrical bore 53 in a mass 54. The mass 54 is that mass which is to be accelerated and decelerated to produce the force which is transmitted to the ground by the seismograph transducer in the manner referred to in the introductory material. Ports 56 and 58 are provided in the mass 54 and communicate with bores 60 and 62, respec tively, which pass radially through the wall of the cylinder sleeve 52. Pairs of O-ring type seals 64 and 66 are provided on opposite sides of the junctions between the ports 56 and 60 and 58 and 62, respectively, to prevent escape of fluid between the mass 54 and the cylinder sleeve 52. A pair of cylinder head sleeve inserts 68 and 70 are inserted in opposite ends of the cylinder sleeve 52 and are retained in place by any suitable conventional means (not shown). O-ring type seals 72 and 74 are provided between the cylinder sleeve 52 and the cylinder head sleeve inserts 68 and 70, respectively, to prevent escape of fluid therebetween. A double-rod-end piston 76 is reciprocally disposed within the cylinder sleeve 52 and is provided with conventional piston rings 78. The piston 76 has rods 80 and 82 which are received in metalto-metal fluid seals within the cylinder head sleeve inserts 68 and 70 at 80a and 82a, respectively.

The sleeve inserts 68 and 70 are secured within the cylinder sleeve 52 in a position substantially as shown in FIG. 3, such that a pair of eccentric grooves 86 and 88 machined in the outer circumference of the sleeve inserts 68 and 70, respectively, register with the bores 60 and 62, respectively. The sleeve inserts 68 and 70 are substantially identical in construction and therefore only insert 70 will be described in detail. It will also be noted that FIG. 4 is taken along reference line 4-4 which passes through the insert 70 and the piston rod 82 although it is to be understood that FIG. 4 is also correct as taken through the port 60 and through insert 68 and piston rod 80, the two fluid ports being identical except for the arrangement of ports 58 and 56 in the mass 54. The groove 88 is eccentric with respect to the axis of the sleeve insert 70 as is best seen in FIG. 4. The maximum cross-sectional area of the eccentric groove 88 is disposed adjacent the bore 62. The eccentric groove 88 preferably has a width along the axial dimension of the sleeve 70 equal to the diameter of the bore 62. The outer diameter of the sleeve insert at point 70a is less than the internal diameter of the sleeve 52 to provide an annular passageway 90 which is in circumferential fluid communication between groove 88 and the face of the piston 76. A similar annular passageway 91 is formed around insert 68.

Therefore, the hydraulic fluid port means comprises the port 58, the radial bore 62 through the cylinder sleeve 52, the eccentric groove 88 and the circumferential annular passage 90. The diameters of the port "58 and the bore 62 are preferably equal to provide a port of constant crosssectional area. The cross-sectional area of the groove 88 generally through reference lines d-d or e--e is preferably approximately equal to one half the area of the bore 62, so that the total cross-sectional area of the fluid port leading away from the terminal end of the bore 62 is constant. The total cross-sectional area of the annular passageway 90 is also equal to the cross-sectional area of the bore 62. Therefore, the cross-sectional area throughout the length of the porting system is constant. The eccentric groove 88 decreases uniformly in depth in each direction around the circumference of the insert 70 so that the volume of the groove decreases at the same rate as the volume of fluid decreases as the fluid simultaneously enters the annular passage 90 as it passes circumferentially around the groove 88.

From the detailed descriptions of the two embodiments of the present invention shown in FIGS. 1 and 3, it will be evident that a novel fluid porting system has been described which has a uniform cross-sectional area throughout the length of the flow path, yet has a total volume which is a minimum for the porting system of a doublerod-end hydraulic actuator in which the fluid port must necessarily be introduced at an angle to the axis of the piston rod. The eccentric groove provides an intermediate transition chamber from the radial bore 42 or 62, as the case may be, to the annular passage around the piston rod so as not to create a restrictive orifice at the transition point between the bore and the annular passageway, as has been the case in previous port systems for linear actuators.

At the same time, the annular passageway can be made of minimum cross-sectional area to reduce the total volume of fluid. The eccentric groove is cheaply and economically machined in that no precision tolerances are required.

The highest frequency at which maximum energy was imparted to the ground was increased from approximately 80 cycles per second to approximately 120 cycles per second in the embodiments described, thereby providing constant energy input throughout the 20-100 cycles-persecond range desired for seismic survey work.

Having thus described specific embodiments of my invention, it is to be understood that various changes and substitutions can be made therein without departing from the spirit and scope of my invention as described by the appended claims.

I claim:

1. In a hydraulic motor having a cylinder and a doublerod-end piston reciprocated at varying frequency within the cylinder by hydraulic fluid at a pressure sufliciently high that the compressibility of the hydraulic fluid reduces the accelerating force produced by the motor at higher frequencies, an improved hydraulic fluid port system having a minimum volume for a given cross-sectional area comprising means forming an annular passage around the piston rod and in fluid communication with the face of the piston and having a given cross-sectional area, means forming a bore having substantially said given cross-sectional area disposed at an angle to the annular passage and connected to receive a hydraulic fluid under pressure, and means forming an intermediate chamber extending circumferentially around the piston rod, the intermediate chamber being in circumferential fluid communication with the annular passage and intersecting the bore to provide fluid communication between the bore and the annular passage, the intermediate chamber having a crosssectional area equal to approximately one half the crosssectional area of the bore at the intersection therewith and having a uniformly decreasing cross-sectional area at circumferentially spaced points around the circumference thereof.

2. In a hydraulic motor having a cylinder and a doublerod-end piston reciprocated within the cylinder by hydraulic fluid at a pressure sufiiciently high that the compressibility of the hydraulic fluid reduces the accelerating force produced by the motor at higher frequencies, an improved hydraulic fluid porting system comprising an annular passage between the rod and the cylinder wall adjacent the limit point of the piston travel, the annular passage having a given cross-sectional area, a radial bore in the cylinder wall communicating with the annular passage and disposed at an angle to the axis of the annular passage, the cross-sectional area of the bore being substantially equal to the cross-sectional area of the annular passage, and an eccentric groove in the wall of the cylinder extendingsubstantially around the circumference of the cylinder and intercepting the bore, the depth of the eccentric groove being a maximum at the point of interception with the bore and having a crosssectional area at the interception with the bore substantially one half the cross-sectional area of the bore.

3. In a hydraulic motor having a cylinder and a double y rod-end piston reciprocated Within the cylinder by hydraulic fluid at a pressure sufliciently high that the compressibility of the hydraulic fluid reduces the accelerating force produced by the motor at higher frequencies, an improved hydraulic fluid port comprising a bore through the cylinder generally perpendicular to the piston rod, sleeve means around the piston rod and within the cylinder having a reduced outer diameter adjacent the cylinder to form an annular passage between the sleeve and the cylinder, the sleeve having a groove eccentric relative to the axis of the sleeve in the outer wall thereof, the groove being in circumferential communication with the annular space and in register at the point of maximum crosssectional area thereof with the bore, the maximum crosssectional area of the groove being approximately one half the cross-sectional area of the bore and the crosssectional area of the bore being substantially equal to the cross-sectional area of the annular passage whereby the hydraulic fluid port will be of substantially constant crosssectional area and will have a minimum volume for the given cross-sectional area.

No references cited. 

1. IN A HYDRAULIC MOTOR HAVING A CYLINDER AND A DOUBLEROD-END PISTON RECIPROCATED AT VARYING FREQUENCY WITHIN THE CYLINDER BY HYDRAULIC FLUID AT A PRESSURE SUFFICIENTLY HIGH THAT THE COMPRESSIBILITY OF THE HYDRAULIC FLUID REDUCES THE ACCELERATING FORCE PRODUCED BY THE MOTOR AT HIGHER FREQUENCIES, AN IMPROVED HYDRAULIC FLUID PORT SYSTEM HAVING A MINIMUM VOLUME FOR A GIVEN CROSS-SECTIONAL AREA, COMPRISING MEANS FORMING AN ANNULAR PASSAGE AROUND THE PISTON ROD AND IN FLUID COMMUNICATION WITH THE FACE OF THE PISTON AND HAVING A GIVEN CROSS-SECTIONAL AREA, MEANS FORMING A BORE HAVING SUBSTANTIALLY SAID GIVEN CROSS-SECTIONAL AREA DISPOSED AT AN ANGLE TO THE ANNULAR PASSAGE AND CONNECTED TO RECEIVE A HYDRAULIC FLUID UNDER PRESSURE, AND MEANS FORMING AN INTERMEDIATE CHAMBER EXTENDING CIRCUMFERENTIALLY AROUND THE PISTON ROD, THE INTERMEDIATE CHAMBER BEING IN CIRCUMFERENTIAL FLUID COMMUNICATION WITH THE ANNULAR PASSAGE AND INTERSECTING THE BORE TO PROVIDE FLUID COMMUNICATION BETWEEN THE BORE AND THE ANNULAR PASSAGE, THE INTERMEDIATE CHAMBER HAVING A CROSSSECTIONAL AREA EQUAL TO APPROXIMATELY ONE HALF THE CROSSSECTIONAL AREA OF THE BORE AT THE INTERSECTION THEREWITH AND HAVING A UNIFORMLY DECREASING CROSS-SECTIONAL AREA AT CIRCUMFERENTIALLY SPACED POINTS AROUND THE CIRCUMFERENCE THEREOF. 